1. Field of Invention
The present invention relates to a structure of an engine mount for a vehicle, and more particularly, to a structure of an engine mount for a vehicle in which a sub-roll rod is additionally mounted based on a structure of a known three-point mounting type engine mount to support an high-output engine more efficiently.
2. Description of Related Art
A vehicle (FF: front engine front wheel drive) of a type in which an engine is disposed in front of a vehicle and a front wheel is driven has an advantage and a disadvantage as compared with other driving types, but the structure of a driving system is simplified to be advantageous in light weight and compactness and is advantageous in broadening an indoor space because a part such as a propeller shaft transferring motive power to a rear wheel is deleted.
In particular, since the FF vehicle is advantageous in terms of productivity, the FF vehicle is widely used in an automobile. However, since a front wheel is both driven and steered, the fluctuation of torque acting on both wheels influences steering and a weight is concentrated in a front part of the vehicle.
That is, a general power transmitting process of the FF vehicle includes (1) an engine, (2) a flywheel of the engine, (3) an input shaft of a transmission, (4) an output shaft of the transmission, (5) a differential gear, (6) a constant velocity joint (CVJ), and (7) a wheel, but since the engine, the transmission (T/M), and the differential gear that are previously integrally coupled are mounted on the vehicle body, the differential gear leans toward one side around the center of the vehicle, as shown in FIG. 1A.
Therefore, the lengths of left and right constant velocity joints are different from each other to cause torque steer steering influencing the steering of a steering wheel.
As described above, in order to solve problems of unequal length driveshafts having both constant velocity joints having different lengths, equal length driveshafts have been ever developed.
A center shaft is mounted between the equal length driveshafts so that the constant velocity joints having the same length are disposed at both sides to be coupled. The center shaft rotates while engaging with the differential gear coupled with the transmission at one side thereof, while the other side is supported on a bearing bracket coupled to the lower part of the engine. In addition, a center bearing allowing rotation of the center shaft is mounted on the bearing bracket.
Meanwhile, automobiles primarily employ monocoque bodies which are light in weight and excellent in productivity instead of frame bodies. The monocoque body is a structure without an additional frame and includes a power train mounted directly on its vehicle body. Therefore, since the vehicle body itself acts as a frame in the monocoque body, suspension and chassis parts are mounted on the monocoque body, respectively, but vibration of the power train (configured by integrally coupling the engine, the transmission, and the differential gear) is prevented from being transferred directly to the vehicle body and a subframe is mounted on a lower part of a vehicle in order to disperse an impact when the vehicle collides.
The subframe may be manufactured in various shapes depending on the power and size of the vehicle, but a power train having an engine of a high displacement and a high torque employs a “#”-shaped subframe in which four bars are coupled to each other to form a rectangle. When the “#”-shaped subframe is installed in a lower part of an engine room of a vehicle body, the power train is seated thereon and mounting members (an engine mount, a transmission mount, a front roll rod, and a rear roll rod) support the power train at four points (a four-point mounting scheme).
In addition, as shown in FIG. 1B, an engine having a low displacement and a low torque has a plate shape which can be fixed to the vehicle body and a steering device can be mounted on, and an “H”-shaped subframe of which an edge protrudes to connect a suspension strut and a knuckle is mounted on the engine. The vehicle employing the “H”-shaped subframe is supported by the mounting members at three points (a three-point mounting scheme). The engine mount and the transmission mount are mounted on at both sides of the vehicle body, respectively, to support the engine and the transmission and a roll rod mounted on the subframe is coupled to the lower part of the transmission in the rear side.
Meanwhile, the four-point mounting scheme is more efficient to suppress noise, vibration, and harshness (NVH) of the vehicle by more efficiently supporting the movement of the power train, but a larger subframe is mounted to increase a total weight of the vehicle.
On the contrary, the three-point mounting scheme has an advantage in that a manufacturing cost is saved, but since the number of mounting points is reduced, there is a limit in supporting the movement of the power train or suppressing the NVH of the vehicle and a larger fatigue is aggravated to the mounts of the engine and the transmission.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.